There is always a need for more durable, ductile, and robust materials for buildings, bridges, and other infrastructure due to the drawbacks of existing construction materials. Some of the drawbacks are the corrosion of steel, the brittle failure of concrete, and the performance instabilities that are caused when exposed to different environments. Thus, an innovative system is required to improve the performance and retain the integrity of structures in a harsh environment. To alleviate the situation, Un-plasticized polyvinyl chloride (uPVC) tubes are used as a confining material and their performance was experimentally evaluated by testing uPVC confined equivalent cylinders. Accordingly, unconfined and uPVC confined equivalent concrete cylinders for five different concrete classes, four types of uPVC tube sizes, and the aspect ratios of two (h/D = 2) were prepared and tested under axial compression loads. The result shows that the uPVC confinement increased the strength, ductility factor, and energy absorption in between 1.28–2.35, 1.84–15.3, and 11–243 times the unconfined levels, respectively. The confinement performed well for lower concrete classes and higher thickness to diameter ratios (2t/D). The post-peak behavior of the stress-strain curve was affected by the 2t/D ratio and the absolute value of the slope decreased as the 2t/D ratio increased. Additionally, the uPVC tube has shown several advantages, such as acting as a permanent formwork, protecting the concrete from chemical attacks, preventing the segregation of concrete, preventing peeling, and taking off concrete cover, decreasing the cross-section, and resulting in lighter sections. The uPVC confinement provided a remarkable improvement on the strength, ductility, energy absorption, and post-peak behavior of concrete. Therefore, uPVC tubes can be used as confining material for bridge piers, piles, electric poles, and highway signboards, where the fire risk is very small, though additional research is required on fire resistance mechanisms, such as wire-mesh reinforced mortar cover.

Background: There is an increased demand for high-performance materials in the construction industry due to the high cost, the difficulty of sourcing and shortcomings of the existing construction materials. Some of the deficiencies are corrosion of steel, brittle failure and rapid deterioration of reinforced concrete structures in a harsh environment. Nowadays, there is also a move from one material to another due to the difficulty of sourcing i.e. timber electric poles to concrete poles due to the difficulty of sourcing native hardwood. These situations have triggered the interest to develop an alternative structural system. Objective: This paper presents the behavior of unconfined concrete, Concrete-Filled Single Skin uPVC Tubular (CFSUT) and concrete-filled double skin uPVC tubular (CFDUT) members under axial compression loads. Method: The unconfined concrete cylinders, CFSUT and CFDUT specimens were prepared from a concrete class of C25 and tested using a UTM machine at a rate of 0.2MPa/s. The parameters considered where thickness to diameter ratio (2t/D), aspect ratio (h/D) and hollow ratio (d/D). Also, a model was developed to predict the peak strength of CFSUT and CFDUT specimens. Results: The result shows that both CFSUT and CFDUT specimens exhibited improved strength, ductility, and energy absorption capacity. For CFSUT and CFSUT specimens, the strength, ductility, and energy absorption capacity increased by more than 1.32, 3.75 and 14.75 times compared to the unconfined concrete specimens, respectively. It is found that the strength decreased as the h/D and d/D ratios increased. The result also shows that the strain of CFSUT and CFDUT at the peak strength increased by more than 3.16 times compared to the unconfined concrete specimens. The proposed model accurately predicted the peak strength with AAE of 2.13%. Conclusion: The uPVC confinement provided a remarkable improvement on the strength, ductility and energy absorption of concrete. Therefore, uPVC tubes can be used as confining material for bridge piers, piles, electric poles, and building columns to increase the strength, ductility and energy absorption of concrete structures.

The behavior of concrete-filled uPVC tubular columns under axial compression loads were studied experimentally by testing columns prepared from five different concrete strength classes. Accordingly, the unconfined, concrete-filled uPVC tube with and without wire-mesh reinforced mortar cover and reinforced concrete columns were evaluated. The main variables considered in this study are concrete strengthðf co Þ, uPVC thickness to diameter ratio (2t/D) and aspect ratio (h/ D). The effect of uPVC confinement on strength, ductility, energy absorption, and post-peak behavior was explored. Also, a model was developed to predict the peak strength. Results show that the uPVC confinement increased the strength, ductility, and energy absorption in between 1.28-2.35, 1.84-15.3, and 11-243 times the unconfined, respectively. The confinement performed well on increasing the strength, ductility, and energy absorption for lower concrete strength and higher 2t/ D ratios. The post-peak behavior of the stress-strain curve was affected by 2t/D and h/D ratios; an abrupt drop in the stress-strain curve was observed in specimens with lower 2t/D and higher h/D ratio. For a given value of concrete strength ðf co Þ, tensile strength f y À Á , thickness (t), diameter (D), and height (h), the stress-strain model ABOUT THE AUTHORS

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